This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Paroxysmal nocturnal hemoglobinuria is an acquired hemolytic anemia characterized by the increased sensitivity of red cells to complement leading to intravascular hemolysis and hemoglobinuria. PNH is due to the expansion of a cell clone that has acquired a mutation in the X-linked PIGA gene. PIGA is an enzyme subunit essential for the synthesis of glycosyl phosphatidylinositol (GPI) anchor molecules. Blood cells derived from the mutant progenitor cell are therefore deficient in all GPI-anchored molecules. The broad long-term objective of our research is to understand the pathophysiology and pathogenesis of PNH. PNH is a chronic disease often associated with substantial morbidity and mortality. Thrombosis is the most frequent cause of death. The pathophysiology of thrombosis in PNH is not understood. We propose that platelets (Plt's) deficient in GPI-linked proteins (PNH phenotype) play a major role in the pathogenesis of thrombosis in PNH. We hypothesize that blood cells with the PNH phenotype not only lack all GPI-linked proteins, but are also deficient in other proteins, whose synthesis or localization is dependent on normal GPI anchor production, and that the deficiencies of these proteins on Plt's might contribute to the prothrombotic risk. In the proposed research we will focus on the molecular aspects of these hypotheses by identifying proteins and protein modification in PNH Plt's that are associated with PNH. First, we will develop reproducible proteomic procedures to isolate and analyze Plt's from normal and PNH patients, and then compare the protein profile from Plts'deficient in GPI-linked proteins with the protein profile of normal Pit's. Finally, we will develop assays to detect and measure candidate proteins or protein modifications specific for PNH cells and verify the differential expression of candidate proteins in a second cohort of patient and control individuals. Our proposed investigations are likely to identify a number of unanticipated proteins, protein interactions, and protein modifications that might significantly advance our understanding of the pathogenesis of thrombosis in PNH and possibly also in other conditions, in which an abnormal clonal hematopoiesis is associated with thrombosis, for example, polycythemia vera or other myeloproliferative syndromes. Established methods for analyzing and comparing the platelet proteome in health and disease might lead to the identification of novel biomarkers useful in evaluating the risk of thrombosis or identify new targets for the development of diagnostics or drugs.